package dontaiguihua;

import java.util.Scanner;

public class fenbolaqieshulie {
	
	
public static int process1(int n) {
	if(n==1) return 1;
	if(n==2) return 2;
	return process1(n-1)+process1(n-2);
}

public static void main(String[] args) {
	Scanner scanner = new Scanner(System.in);
	int n = scanner.nextInt();
	System.out.println(process1(n));
}
}
